1. Field of the Disclosure
The present disclosure relates to switching power converters, and more specifically to improved on-time compensation for switching power converters.
2. Description of the Related Art
Switching power converters are used in many different electronic devices to generate a regulated output voltage from an input voltage by cyclically turning a switch on and off to adjust a level of the regulated output voltage. Some power converters operate in discontinuous current mode (DCM). In DCM, the switch is turned on to allow current to flow into an inductor of the switching power converter. The switch is then turned off to allow current to flow out of the inductor and out towards the load, thereby resetting the inductor. A dead time is inserted after the reset time that limits the switching frequency of the switch. If there is voltage ringing at the top side of the switch, the length of the dead time can be modified to allow the switching to occur at the valley of the ringing.
Inserting the dead time is useful for reducing an amount of power lost in the switch itself, but has the negative side effect of reducing the power factor of the switching power converter. The power factor of a power converter impacts the power delivery system, such as the utility transmission lines that supply AC power to the power converter. If the power factor of a converter is low, the utility company must waste more power to deliver the required power to a load. To maximize the power factor, the average input current to the switching power converter should be proportional to the input voltage. In power converters that have a fixed on-time and no dead time, the average input current is naturally proportional to the input voltage and good power factor can be achieved. However, in power converters that have a dead time, the length of the dead time affects the level of the average input current and causes the average input current to deviate from being proportional to the input voltage. As a result, the power factor of the power converter is reduced by the dead time.